Expand grouping view with customer label

As an admin, I want to be able to filter and group by customer labels within the "grouping" view in the new overviews view, so that I can easily generate overviews by customer segment, which helps me prepare for invoicing.

Explanation:

I use customer labels to categorize customers (for example, by region, customer type or contract type). By being able to group on these in reports, I can create faster and more focused billing overviews.